How chromium is made

Most chromium never becomes a pure metal. It is smelted with iron into ferrochrome and goes straight into stainless steel.

stations: 6
things upstream: 24
raw sources: 13
steps from the ground: 5

The short version

Chromium is made from chromite ore. For stainless steel, chromite is smelted with coal and coke in an electric arc furnace into ferrochrome, an iron-chromium alloy with 50 to 70 percent chromium. Pure chromium takes a longer path: the ore is roasted with carbonates, leached to a chromium compound, and reduced with aluminum.

Mine the chromite

Chromite, an iron-chromium oxide, is dug mostly in South Africa and Kazakhstan. About 28.8 million metric tons of marketable ore were produced in 2013.

Goes in
Chromite
Smelt it in an arc furnace

Huge electric arcs between electrodes in the furnace bottom reach about 2,800 °C. Coal and coke take the oxygen from the chromite, and an iron-chromium alloy forms.

about 2,800 °C

Goes in
Coke
Tap and crush the ferrochrome

When enough has gathered, the tap hole is drilled open and molten ferrochrome and slag rush down a trough. The metal freezes in large castings that are crushed for sale. This alloy is 50 to 70 percent chromium, and stainless steel is its main customer.
Roast the ore for pure metal

For metal free of iron, chromite is heated in air with calcium carbonate and sodium carbonate. The chromium turns into a soluble form, and the iron becomes stable iron oxide that stays behind.

Goes in
Soda ash Limestone Air
Leach and convert to oxide

Hot leaching washes the soluble chromium compound away from the iron. It is converted to dichromate, and carbon then reduces that to chromium(III) oxide.

Goes in
Water
Reduce it with aluminum

In an aluminothermic reaction, aluminum powder takes the oxygen from the chromium oxide and leaves chromium metal.

Goes in
Aluminum

End of the lineChromium Next it goes into hip implant, hard drive, stainless steel and 11 more.

Worth repeating

Stainless steel and chrome plating together account for 85 percent of commercial chromium use.
Chromium is the third hardest element, after carbon in the form of diamond and boron.
Chromium(III) is considered non-toxic, but hexavalent chromium, found in chromates, is toxic and carcinogenic.